Field of the Invention
The present invention relates to residual chlorine measuring apparatus and a method of measuring residual chlorine. To be more specific, the present invention relates to a residual chlorine measuring apparatus and a method of measuring residual chlorine that are suitable for measuring residual chlorine in water in which a stabilizing agent that reduces degradation of a chlorine-based oxidizing agent is added to a chlorine-based oxidizing agent.
Description of Related Art
Residual chlorine is the effective chlorine having a disinfectant action, which remains in water after chlorination, and is classified into free residual chlorine such as hypochlorous acid and combined residual chlorine such as chloramines or chlorosulfamates. Both free residual chlorine and combined residual chlorine have a bactericidal capacity due to oxidation.
A halogen-based oxidizing agent such as a hypochlorite generates free residual chlorine and has a high bactericidal capacity. However, the halogen-based oxidizing agent is likely to be degraded by an ultraviolet ray and thus has low stability in water. In addition, a problem arises in that the halogen-based oxidizing agent has high oxidative power, and thus has high corrosivity.
Hence, in order to reduce the degradation of a chlorine-based oxidizing agent such as a hypochlorite, a technique in which a sulfamic acid salt or the like is added as a stabilizing agent is known. When a sulfamic acid salt is added to a hypochlorite, an N-monochlorosulfamate or an N, N-dichlorosulfamate is formed. In other words, combined residual chlorine is produced.
Combined residual chlorine has a low oxidative power; however, reaction of the combined residual chlorine with water makes it possible to produce free residual chlorine for a long period of time.
In addition, in order to further stabilize a chlorine-based oxidizing agent, a technique in which sulfamic acid or a sulfamic acid salt, and an azole-based compound such as benzotriazole are added to a chlorine-based oxidizing agent is known (Japanese Patent No.3832399). The benzotriazole or the like is used to achieve corrosion prevention or the like of a pipe or the like, and thus, chlorination target water contains benzotriazole in some cases.
In chlorination, it is important to measure a residual chlorine concentration and to adjust an amount of the oxidizing agent used. As a method of measuring the residual chlorine concentration, an o-tolidine colorimetric method (OT method) or a diethyl-p-phenylenediamine colorimetric method (DPD method) is known. In addition, the residual chlorine concentration measurement may be performed by a polarographic method (for example, Japanese Unexamined Patent Application, First Publication No. 2005-62133).
The residual chlorine concentration measurement performed by a polarographic method is a method suitable for continual measurement or automation.
However, according to findings of the inventors, in a case of water in which benzotriazole or the like is contained, a sufficient current output is not acquired even when the measurement of the residual chlorine concentration is performed by a polarographic method.
According to research of the inventors, in a case of water in which benzotriazole or the like is contained, it is found that a surface of a detection electrode is instantaneously covered with a coating of benzotriazole or the like, which inhibits the detection electrode from reacting with the residual chlorine.
In consideration of the circumstances described above, an object of the present invention is to provide a residual chlorine measuring apparatus and a method of measuring residual chlorine which use a polarographic method, in which it is possible to calculate a total residual chlorine concentration of water in which benzotriazole or the like is contained.